1. Field of the Invention
The present invention relates to an overturn prevention control device that controls balance to prevent overturning of a body that is capable of freely laterally inclining such as, for example, a two-wheel vehicle or a biped robot.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2003-190654 describes a two-wheel traveling toy including a steering portion, a front wheel steerable by the steering portion, a rear wheel, a flywheel swinging in accordance with the direction of the front wheel, a first driving portion arranged to drive the flywheel, and a second driving portion arranged to drive the rear wheel. The two-wheel vehicle is resistant to overturning while traveling due to the gyro effect of the flywheel produced by changing the direction of the flywheel in accordance with the direction of the front wheel.
However, in the aforementioned two-wheel traveling toy, because the direction of the flywheel is merely changed in accordance with the direction of the front wheel, although the vehicle is prevented from overturning during normal travel by steering, it is difficult to prevent the vehicle from overturning when stopped or while moving at a very low speed by steering alone. As a result, there is a problem in that overturning cannot be effectively prevented.
Japanese Unexamined Patent Application Publication No. 11-47454 describes an inversion control toy in which overturning is prevented by inputting an inclination detected by an inclination detecting sensor into a control circuit, driving of a motor using the control circuit, rotating a high-inertia rotor using the motor, and generating a reaction couple by increasing the number of revolutions of the rotor in the direction opposite to the direction in which the inclination is to be corrected. This inversion control toy maintains its balance by controlling the revolutions of the rotor, such that overturning is prevented even when stopped or when the toy moves at a very low speed.
The above-described inversion control toy uses, as the inclination detecting sensor, an optical sensor that detects an inclination using a photo detector receiving light reflected from the surface of the floor after being emitted from a light-emitting device. However, in practice, it is not easy to accurately detect the inclination. For an inclination detecting sensor that uses a light-emitting device and a photo detector, although there is no problem when the surface of the floor that is to reflect light is flat, it is impossible to accurately detect the inclination when the surface of the floor is uneven or the floor is not present on both sides (for example, when the toy crosses a narrow bridge).
In addition, the above-described inversion control toy detects the inclination by obtaining the difference from the amount of received light in an upright state as the reference amount. However, the upright state (in a vertical direction) is not always a balanced state. For example, when the position of the center of gravity of the toy is laterally displaced from the central position or when the toy is subjected to a side wind, a state that is slightly inclined relative to the vertical direction is a balanced state. In this case, although that balanced state (angle) should be used as a reference position, the vertical direction is used as the reference position in the above-described method. Therefore, the toy may be unable to maintain its balance and may overturn.
One possible method of detecting the inclination of a body is detecting the angular velocity using an angular velocity sensor, integrating the detected value, and thereby estimating the inclination. However, in the method of integrating the output angular velocity, a problem arises in that noises or offsets are accumulated and it is not possible to continue to estimate an inclination angle and prevent overturning. Another device for detecting an inclination is an inclination sensor that uses a weight. However, in this case, the inclination corresponding to a balanced state cannot be detected, and additionally, responsiveness is poor, resulting in a disadvantage in that the inclination cannot be immediately detected.